1. Technical Field
The present invention relates to an acceleration sensor and to a method of fabricating an acceleration sensor.
2. Related Art
Wafer-Level Chip Size Packages (WCSP) and plastic packages are effective as a way to realize more compact and lower cost electrical components, including ICs.
For example, in Document 1, G Li and A A Tseng, Low stress packaging of a miromachined accelerometer, IEEE Transactions on Electronics Packaging Manufacturing, Vol. 24, pp 18-25, January 2001, a configuration is described in which an acceleration sensor is sealed on a plate produced from silicon, and covered over with a gel. The acceleration sensor is cushioned from external stress by the gel and the silicon plate, suppressing influence on the sensing characteristics of the acceleration sensor.
A structure exists in which an acceleration sensor and a control IC are stacked and sealed with a resin (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 2008-026183).
Furthermore, a pressure sensor structure is described in which thickened portions are provided at two locations on the external periphery of and inside of a sensor device, and external stress is borne by a leg portion (see, for example, JP-A No. 7-280679).
There is also a description relating to an external force detection sensor in which an SOI substrate is employed, wherein a flexible portion forming region of the SOI substrate is provided with a groove surrounding the entire periphery along a substrate front surface (see, for example, JP-A No. 2008-170271).
Furthermore, there is a description of a stress cushioning portion structure, wherein a groove is provided cut into the rear face side of a substrate around the external periphery of a device, and a groove is provided cut into the rear face of a support portion (see, for example, JP-A No. 2000-187040).
However, with the structure described in Document 1 above, while the stress to the acceleration sensor from outside is cushioned by the silicon plate, and influence on the sensor characteristics are suppressed, after substrate mounting, external stress from a direction along the substrate surface cannot be completely blocked from the detection portion of the sensor, and a concern exists that stress will cause a change in characteristics.
Furthermore, in the configuration of the fifth exemplary embodiment described in JP-A No. 2008-026183 above, FIG. 5, there is an SOIC package configured from a metal plate (bottom plate) and sealing resin, and since the sealing resin covers the outside of a support body, there is a concern that stress from the sealing resin is transmitted to the support body or a beam portion, with the possibility that stress might cause a change in characteristics of the sensor.
Furthermore, in the structure described in JP-A No. 7-280679, the leg portion on the outermost periphery is physically connected through a thinned portion to a diaphragm, and since the structure is not completely separated, when external stress is borne by the leg portion, the stress through the thinned portion is transmitted to the thickened portion and to the diaphragm, with a concern of this causing of a change in characteristics.
Furthermore, in the structure described in JP-A No. 2008-170271, the structure does not have the fixed portion completely surrounded by the groove and blocked off from the outside, and in side view the fixed portion is still connected to the outside, such that external stress is not completely blocked by the groove, to give a structure where there is concern of the external stress being transmitted to the fixed portion.
Furthermore, in the structure described in JP-A No. 2000-187040, a groove is provided cut into the rear face of the support portion as a stress relief portion, however the structure is such that external stress to the sensor chip cannot be completely blocked from the flexible portion by the cut in groove, and there is a concern that the external stress will cause a change in characteristics.